so I ran the install routine from pi-hole.net - had to change the dashboard url (admin/index.php vs pihole/index.php) - and it's blocking ads, as long as I manually add the dns to my network settings. But not when I set it from the router... hmmm...

Ah, Dietpi... They have a customized version of Pi-hole, which we don't manage or support. I would recommend uninstalling it and installing the official version with curl -L https://install.pi-hole.net | bash. That version that they have is not usually updated when we update ours, and has some other oddities.

You may have to wait for a little bit, or reboot your devices, until they start using the new DNS server.

There is a possibility, if no devices are getting the new DNS server, that for some reason it doesn't play nice with using local addresses for DNS. If you are still unable to get your devices to have the new DNS server

Oops... clicked enter.

...within something like half an hour, then look for a setting called DNS rebind or DNS rebind protection. That prevents it from using local servers as DNS, so you have to turn it off.

There are a few routers that don't have the option, like a certain netgear router I was struggling with, so in that case either install a new router firmware or manually set Pi-hole on each device.

actually, as silly as it seems, that seems to have fixed it. when you set WAN DNS to 'no' it gives you two DNS server fields. I put the pi in the first, left the second blank, applied. The router restarted and seems to be working